The invention relates to a solid-bed reactor for biological sewage treatment with a sewage intake above the solid bed, an intermediate floor with floor jets for back washing the solid bed, and aeration orifices.
Apparatus for the filtration and biological treatment of sewage is known which has a flooded, aerated solid bed and in which the raw water flows in countercurrent to the air introduced (see for example M. Payraudeau, J.-Y. Bontonou "Traitement biologique a basse temperature selon un procede de filtration biologique aeree: le BIOCARBONE", ("Low temperature biological treatment by a method of aerated biological filtration: BIOCARBONE") Les Eaux Usees Diluees, 1990, p. 395). The aeration orifices in the "Biocarbone" method are approximately 30 cm above the intermediate floor, within the solid bed. The oxygen introduced and the biodegradable constituents of the raw water lead to the propagation of micro-organisms which colonise the surfaces of the packing elements. Periodically some of the growing biomass must be removed. This is done with an air/water mixture which is driven through the solid bed by means of the floor jets in the intermediate floor. Along with the biomass this removes particles which have settled out of the raw water in the solid bed.
German Offenlegungschrift 33 21 436 discloses apparatus of the type described above in which the intermediate floor contains apertures for aeration; aeration orifices of a special design provide an oxygen supply which is largely unaffected by variations in the degree of clogging of the solid bed. The air may be supplied by way of an air cushion below the intermediate floor, the cushion being only a few centimeters deep. French Patent Specification 2 596 385 proposes a floor jet of substantially conventional construction with an integral aeration orifice in the form of a small hole. With this simple and apparently very convenient floor jet (orifice), however, as experience shows, a stability problem occurs, making such floor jets impossible to use. This problem will be explained below with reference to the drawings.